Not since the Great Rubber Engine Mounting of 2004 has such a big change been made to the Sportster. In fact, the big change came last year, when H-D used a stunning new technology on its new XR1200 Sportster, which everybody liked so well H-D decided it might not be a bad idea to use it on some of the other bikes, too. That’s right, it’s the radial motorcycle tire, a recent invention of the Michelin Tire Company, circa 1984.

The radial motorcycle tire uses its unusual construction to lay down a bigger contact patch for more grip, while the reduced friction of its inner plies typically allows it to run cooler than a bias-ply tire, thus better suiting the radial to high-speed applications. More grip and better high-speed handling are things the venerable 883 needs about as much as a housecat needs a wristwatch, might be your initial reaction but, in fact, the new SuperLow is a much nicer machine to ride as a result of its new rubber and the changes that accompany it—which include longer-travel shocks out back wrapped in progressive springs, a restuffed seat, a new handlebar bend and even revised steering geometry.

It all, not surprisingly, adds up to a Sportster that rides smoother and handles better. It’s a little difficult to say what percentage of the smooth new ride is due to the tires, and what part is down to the new shocks and seat foam, but whatever the case, the SuperLow XL883L much more effectively dispatches the very bumps your coccyx cringes to recall riding over on last month’s Iron 883 test unit. Over bad pavement, where all previous Sportsters feel somewhat like riding a depleted uranium bullet through an armored outhouse door (at around 550 pounds, they’re dense little bikes), the SuperLow feels more like a modern motorcycle rolling over some bumps. Nice work.

Compared to the 19-inch front wheel assembly (wheel, tire, brake rotor) it replaces, the new 120/70ZR18-Michelin-shod front is less than a pound lighter, but its smaller diameter reduces spin inertia by about 25 percent, according to H-D’s Matt Weber, Principal Engineer of Vehicle Dynamics. Out back, where a 150/60ZR17 radial on a 4.5-inch wheel replaces the old 150/80-16 bias-ply tire, the difference is more dramatic: a weight reduction of 5 pounds and 38 percent less spin inertia. That much less unsprung weight jacking up and down a few inches from your butt is a difference you can feel in a number of ways. Not only does it help deliver a better ride, the lighter weight of the new tires/wheels at both ends of the bike notches up all aspects of performance. The SuperLow’s quarter-mile run of 14.42 seconds at 91.11 mph is three-tenths quicker and 5 mph faster than what the Iron 883 pulled off. The 0-60-mph time is fourth-tenths quicker at 6.1 seconds. It can’t hurt that this bike spun the dyno 5 horses harder than our last 883 Sportster, to the tune of 49.9 hp.

Uh, where were we? Tires, right… The overall diameter of the new radial out back is only a few inches less than that of the old bias tire (it looks like more), so one tooth bigger on the countershaft sprocket keeps gearing close to same-same.

Engineer Weber, who also worked on the XR1200, compliments Michelin engineers on how they listened to and worked closely with H-D to produce a pair of tires that really complement the Sportster—a front that gives great steering feel and precision, and a rear that works with the front to provide confident, steady-state cornering.